Radio frequency antenna



ocvt' 6, 3 H. FQENGELMANN 2,654,842

RADIO FREQUENCY ANTENNA N Fil ed July 21, 195i 2 sheets -sheet .1

4 I V 4a 9 a I -2 2 I \J 3 V INVENTOR HERBERT EWGELMANN BY ATTORNEY Oct. 6, 1953 H. F. ENG ELMANN RADIO FREQUENCY ANTENNA 2 Sheets-Sheet 2 Filed July 21, 1951 INVENTOR Ht 'RBERT F. ENGELMANN 'ATTORNEY Patented Oct. 6, 1953 RADIO FREQUENCY ANTENNA Herbert F. Engelmann, Mountain Lakes, N. J., assignor to Federal Telecommunication Laboratories, Inc., Nutley, N. J a corporation-of Delaware Application JulyZl, 1951, Serial No. 237,857

13 Claims.

This invention relates to radio antenna systerns and more particularly to a slot form of antenna particularly useful for radiation of microwave energy.

Microwave antenna systems heretofore required expensive conductor systems employing waveguides or coaxial cables. As technical development reached into higher and higher frequencies, the precision requirements of these types of radiation systems have become very exacting thereby rendering dinicult the manufacture of satisfactory microwave antennas.

One of the objects of this invention is to provide a simplified form of microwave antenna system which does not require the precision and exactness of microwave antenna systems heretofore believed necessary.

Another object of the invention is to provide a microwave antenna system that may employ as a part of the radiation system a wall of the chassis or other apparatus associated therewith.

Still another object .of the invention is to provide a microwave antenna system which is of a character readily adapted for use of printed circuit techniques. 1 i

A further object is to provide a coupling arrangement utilizing the slot radiation feature of the invention.

One of the features of the invention is its utilization of a basic principle present in a theoretically perfect parallel line type of transmission system. This principle is discussed at length in the copending applications of D. D. Grieg and H. (F. Engelmann, Serial No. 227,896, filed May 23, 1951, and Serial No. 234,503, filed June 30, 1951. The principle discussed in these copending applications is utilized in this invention by employing as theradiating element of the antenna system a conductor hereinafter referred to as a line conductor which is small in width or diameter compared to a second conductor, hereinafter referred to as the groundconductor. is small compared to the width of the line conductor. The ratio of thedimensions of these two conductors is of the order of one to two or one to three, although, it may be greater if circumstances provide a wider ground conductor surface.

The above-mentioned and other features and Also the spacing between the conductors .obiects'of this invention and the manner of attaining them will become :moreapparent by referenceto the following description taken in conjunction with the accompanying drawings, wherein:

Figs. 1 and 2 are plan and side views, respec- 2 tively,of an antenna array embodying the principles of the invention;

Fig. 3 is a front view of a more complex antenna array;

Fig. 4 is a front View of an antenna according to the invention which radiates circularly polarized energy;

Figs. 5 and 6 represent rear and side views, respectively of an antenna array according to the invention employing printed circuit'techniques;

Fig. '7 is a front view of an antennaarray similar to the one shown in Fig. 3 together with a balanced coupled line therefor; and

Figs. 8 and 9 are longitudinal and cross-sectional views, respectively, taken along lines -8--'8 and 9-9 of Fig. 7.

Referring to Figs. 1 and 2 of the drawings, a first or line conductor I is shown proximate to a second or ground conductor 2 which is pierced therethrough with openings 3 for the purpose of radiating energy propagated along conductor I in the region of the concentrated electric field betweenconductors i and 2. While the openings here and in other embodiments are shown as rectangular slots, other shapedopenings such as round, elliptical, square or even irregular will serve. The line conductor 4 is supported by a termination 4 which may terminate the conductor in its characteristic impedance if it is desired that no standing waves be present in the line conductor, or the termination 4 may simply constitute a mechanical sup-port for the conductor. The termination 4, for example, may comprise a short to conductor 2 for phase control purposes. A coaxial line 5 is shown energizing the antenna, although it will be understood that this may be a waveguide or other type of transmission system, such as the line-ground type discussed in our aforesaid copending applications.

Fig. 3 shows a more complex antenna array employing a branched line conductor 5 proximate to a number of openings 1 which determine the radiation pattern and polarization of the antenna. Terminations B are shown for the line conductors 6 while the ground conductor 9 constitutes the plate in which the openings 7 are pierced. The branching line conductors G are "sochosenin size and spacing with respect to the plate conductor Sthat they combine to match the impedance of the coaxial line '5.

If desired, a matching transformer may be used at the junc tion.

The pattern of radiation for the antennas of Figs. 1, 2 and3.may be adjusted by variation of one or more of the following parameters; the wave form along the line conductors I or 6, the

spacing between the line conductors I, 8 and the ground conductors 2, 9, the shape of the openings 3 and I and the relative location of these openings. A conductor carrying microwave energy proximate to a ground conductor may produce no radiation if the distance separating these two conductors is a very small fraction of the wavelength of the microwave energy. If, however, the spacing between these conductors is altered, for example, by making a number of openings in one of the conductors, radiation has been found to occur from the areas defined by these openings. A number of openings placed at, for example, points one wavelength apart along the line conductor will produce a radiation pattern similar to that from a number of antennas energized in phase. If, however, the openings are placed in a more general arrangement along the line conductors an antenna radiation pattern may be formed which is of arbitrary form. Accordingly, Figs. 1, 2 and 3 show two examples of antenna arrays embodying these principles of the invention.

Fig. 4 shows an embodiment of the invention by which circularly polarized microwave radiation may be obtained. A line conductor Hi is shown proximate to two openings ii and E2 in the ground conductor, which'are of rectangular form, disposed at right angles to each other and spaced apart approximately one quarter wavelength or an odd multiple thereof. The two openings ll and i2 are of essentially slit character and produce radiation which is polarized in the direction of the slit which is at 90 with respect to that from the other opening due to the fact that the line conductor it is disposed at right angles with respect to its position proximate the other opening. More than two openings may be provided if desired in order to obtain both circularly polarized'energy and a prescribed amplitude radiation pattern.

Figs. 5 and 6 show an embodiment of this invention wherein the line conductor 13 is a strip of conductive material, printed, embossed 0r photographically applied onto one side of a strip of dielectric M, the opposite side of which is similarly covered by the ground conductor 15 Which possesses a number of openings 16 which define the radiation pattern of the antenna. Termination means are shown as a matching capacitive reactance in the form of an area of conductive material having capacity with plate I5. If desired, a matching inductive reactance may be provided by a proper stub length [3a of line :3. The line conductor [3 may be suitably deformed as in Fig. 4 if radiation is desired which is not plane polarized. Correspondingly,

the line conductor l3 may be branched as in V Fig. 3 to provide for a more complex antenna array and resultant radiation pattern.

In Figs. 7, 8 and 9 an antenna array similar to that shown in Fig. 3 is illustrated together with two antenna coupling lines which are balanced at 180 phase relation. The antenna comprises a ground conductor [8 in the form of a plate and two line conductors l9 and 20 supported on layers of insulation 21 and 22, the layers 2| and 22 being on opposite sides of the plate conductor is. The plate I8 is provided with two rows of antenna slots 23 and 24 across which the conductors l9 and 20 extend. These slots are fed by the microwave energy conducted by the lines 19 and 20 with respect to the conductor plate 18. The lines I9 and 2c are coupled to a main lead line comprising a strip of con ductive material 25 which is connected directly to the plate conductor l8. Disposed on this strip is a layer of dielectric material 26 which supports the line conductor 20 which is also supported by the dielectric 22 on the antenna plate. The line conductor [9 extends down across the opposite side of the conductor strip 25 and is supported thereon by a layer of dielectric material 21, the conductor being terminated by a short 23 connecting it to the conductor strip 25. The two line conductors are coupled by means of a slot 29 contained in the ground conductor 25, the slot being located approximately one-quarter of a wavelength from the short 28. The dielectric materials 25 and 21 of the transmission lead line are selected of different dielectric quality and of suflicient lengths so that the phase of the voltages on the two lines 59 and 20 are substantially out of phase thus providing a balanced system.

It will be noted that the transmission line 20 is on the side of the ground plate I8 opposite from the line conductor I9. This makes little difference in the radiation of the slots since the slots radiate in both directions from the plane of the plate I8 regardless of from which side the slots are fed. The ends of the lines l9 and 20 are terminated in matched conductive reactance sections 30 and 3|.

While'I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made by way of example only and not as a limitation to the scope of my invention, as set forth in the objects thereof and in the accompanying claims.

I claim: 7 r

1. In a microwave system, a first conductor, a second. conductor of planar shape wider than said first conductor, said second conductor being exposed conductively to open space on opposite sides of the plane thereof and having an opening therethrough across which extends said first conductor whereby part of the microwave energy propagated along said conductors is radiated by said opening into open space on both sides of the plane of said second conductor.

2. In a microwave system according to claim 1 further including a layer of dielectric material supporting said first conductor in spaced relation on said second conductor.

3. In a microwave system according to claim 1, wherein said second conductor includes a series of openings across which said first conductor extends.

4. In a microwave system according to claim 1, wherein the second conductor includes two rows of openings and the line conductor is divided into two branches, a branch being extended crosswiseof one of said rows, and the other branch being extended crosswise of the other of said rows.

5 In a microwave system; a first conductor, a second conductor of planar shape wider than said first conductor, said second conductor having two rows of openings and said first conductor being divided into two branches, onebranch being disposed on one side of said second conductor and extended crosswise of one of said rows and the second branch being disposed on the opposite side of said second conductor and extended crosswise of the other of said rows, whereby microwave energy propagated along said branches is radiated by said openings.

6. In a microwave'system accordingto claim 5, further including a transmission line comprising a line conductor and a ground conductor to which a ground potential is applied, said ground conductor being wider than said line conductor, one of said branch conductors being connected to said line conductor, said second conductor being connected to said ground conductor and means for coupling said second branch conductor to said line conductor.

7. In a microwave system according to claim 6, wherein the means for coupling said second branch conductor includes an opening contained in said ground conductor with said line conductor extending across said opening on one side of said ground conductor and said second branch conductor extending across said opening on opposite sides of said ground conductor.

8. In a microwave system according to claim 7, further including a layer of dielectric material disposed on one side of said ground conductor to support said line conductor in spaced relation thereto and a second layer of dielectric material on the opposite side of said ground conductor to support said second branch conductor in spaced relation thereto, the dielectric quality of said two layers being different and of such length as to produce a phase difference in the microwave energy of said two branched conductors.

9. In a microwave system, a first conductor, a second conductor of planar shape wider than said first conductor, said second conductor having an opening therethrough across which extends said first conductor, and a, third conductor disposed on the side of said second conductor opposite to said first conductor, said third conductor being extended across said opening whereby microwave energy is coupled from said first conductor to said third conductor for propagation along said third conductor with respect to said second conductor.

1'0. In a microwave system according to claim 9, wherein said third conductor includes means for terminating said third conductor a distance beyond said opening equal to substantially onequarter wave or an odd multiple thereof of said microwave energy.

11. In a microwave system according to claim 9, further including a layer of dielectric material supporting said first conductor in spaced relation to said second conductor and a second layer of dielectric material supporting said third conductor in spaced relation with respect to said second conductor.

12. In a microwave system according to claim 1, wherein said second conductor includes two openings of slot configuration with one slot disposed at an angle to the other slot.

13. In a microwave system according to claim 12, wherein said angle is substantially whereby radiation of circular polarization. is obtained.

HERBERT F. ENGELMANN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,226,479 Pupp Dec. 24, 1940 2,297,202 Dallenbach et a1. Sept. 29, 1942 2,575,571 Wheeler Nov. 20, 1951 

